Blender not exporting mesh properly
The reason you are seeing the cube instead of the chair is because there is a Cube on layer 1. Your chair is on layer 3. You only had layer 3 visible which is why you did not see the cube even though it is there.
There are two ways to avoid this problem in the future:
Method 1 - deleting the cube

Go to layer 1 by pressing 1 on your keyboard

Select the cube and delete it, X


Method 2 - only exporting the needed meshes

Select the chair and any other items you wish to export

In the export dialog check Selection Only



Once you do this you can import the chair and it will work like you expect it to.